This invention relates to a rope traction device and, more particularly, to an improvement in a rope traction device suitable for use in construction, loading and unloading and conveying machines including moving scaffolds, elevators and cranes.
A rope traction device is a type of winding instrument used for construction, loading and unloading and conveying machines and is capable of moving up and down along a rope with the rope wound around its sheave by only one or few windings and without winding the rope around and feeding it from a drum.
An example of a prior art rope traction device used for moving up and down a moving scaffold for performing a work along an exterior wall surface of a building is shown in FIG. 7. This rope traction device includes a frame 1, a drive shaft 2 mounted on the frame 1, a motor (not shown) provided on the outer periphery of the drive shaft 2 through a bearing and a sheave 4 driven by this motor. The rope traction device further includes a traction mechanism 6 for holding a rope 5 wound about this sheave 4 by one winding for preventing the rope 5 from slipping off the sheave 4 and further a brake mechanism (not shown).
This traction mechanism 6 includes an L-shaped pivoting arm 8 provided in the vicinity of a point at which the rope 5 is disengaged from the sheave 4. A pair of rollers 9, 9 are rotatably mounted at one end of the pivoting arm 8 to press the rope 5 inwardly from a straight tightened state thereof. Another pair of rollers 10, 10 are rotatably mounted on a pivoting arm 11 which is pivotably mounted at the other end of the pivoting arm 8.
According to this structure, as the rope 5 becomes straightly tightened, the rollers 9, 9 which are in contact with the rope 5 are pushed by the rope outwardly and the pivoting arm 8 thereby is pivoted in a counterclockwise direction to cause the rope 5 to be pressed by the rollers 10, 10 to the groove of the sheave 5.
In the traction mechanism 6 described in which the rope 5 is pressed against the sheave 4 by the pair of rollers 10, 10 mounted on the pivoting arm 11, bending moment is repeatedly applied to the rope 5 at points of contact with the V-shaped groove of the sheave 4 at two positions at which the rollers 10, 10 tend to slip sideways by force applied in transverse direction by twisting of the rope 5. For these reasons, wear occurs in the rope 5 and the life of the rope 5 thereby is shortened.
It is, therefore, an object of the invention to provide a rope traction device capable of producing a large rope pressing force and ensuring a prolonged life of the rope without causing wear in it.